In recent years, attention has focused on sugar chains as biological molecules in addition to nucleic acids (DNA) and proteins.
It is understood that sugar chains present in membrane proteins and outside the cell participate in intercellular recognition and interaction. Moreover, it is understood that changes in intercellular recognition and interaction cause cancer, chronic disease, infection and aging.
For example, changes in sugar chain structure are known to occur in cancerous cells. Also, it is known that pathogenic viruses including influenza viruses infiltrate and infect cells by recognizing and binding to specific sugar chains.
It is understood that many sugar chains exist in the body in the form of glycoproteins and glycolipids and perform physiological functions by means of intercellular recognition and interaction and the like.
Sugar chains in the body not only have a variety of structures, but are present in tiny quantities and are often bound to proteins and the like, so generally, numerous steps are often required for purification thereof. The operations of sugar chain extraction and purification are known to be difficult.
With recent research advances in the field of sugar chemistry, research for enzymes which substitute human sugar chains for sugar chains of glycoproteins having yeast sugar chains has been accelerated, and human sugar chains can now be substituted for yeast sugar chains with high efficiency. It is possible that the cost to manufacture glycoproteins by such method becomes less expensive than that to manufacture glycoproteins having human sugar chains using animal cells.
For example, erythropoietin having a human sugar chain can be manufactured by substituting a human sugar chain for a yeast sugar chain of erythropoietin expressed in yeast.
According to such method, erythropoietin having a human sugar chain can be provided cheaply and in large quantities, with lower manufacturing costs than conventional methods using animal cells. Moreover, the sugar chain structures are uniform, ensuring the quality of a drug product. Thus, methods of supplying human sugar chains and substituting human sugar chains for the yeast sugar chains of glycoproteins expressed in yeast are considered extremely effective in the manufacture of antibody drugs and physiologically active proteins.
However, no method has yet been established for providing human sugar chains in large quantities, so there is demand for establishment of such methods.
In recent years, egg yolks have gained attention as a source of supply of human sugar chains. Egg yolks mainly contain complex-type biantennary N-glycans that are same as human sugar chains, thus human sugar chains could be supplied using egg yolks as the source if these sugar chains could be extracted efficiently and in large quantities.
For example, Patent Document 1 discloses preparing an 11-sugar sialylglycopeptide from defatted chicken egg yolks (powder).
Moreover, Non-patent Document 1 discloses obtaining a sugar chain peptide (SGP: sialylglycopeptide), which is extracted from the water-soluble fraction of chicken eggs. The SGP is a compound in which a peptide residue of a peptide chain consisting of 6 amino acid residues is bound to the reducing terminal of a complex-type glycan chains consisting of 11 sugar residues, which is human sugar chain.
Further, Patent Document 2 discloses a method of manufacturing a sialic acid-containing oligosaccharide by extraction with water or a salt solution from defatted bird egg yolks.